Age Structure and Age Pyramids

An Overview of the Concept and Its Implications

An age pyramid shows the population structure of the United States in 2014.
This age pyramid illustrates the age structure of the population of the United States in 2014. Data derived from the CIA World Factbook. IndexMundi.com

The age structure of a population is the distribution of people among various ages. It is a useful tool for social scientists, public health and health care experts, policy analysts, and policy-makers because it illustrates population trends like rates of births and deaths. These are important to understand because they have a host of social and economic implications in society, like understanding the resources that must be allocated for childcare, schooling, and healthcare, and the familial and greater social implications of whether there are more children or elderly in society. In graphic form, age structure is portrayed as an age pyramid that shows the youngest age cohort at the bottom, with each additional layer showing the next oldest cohort. Typically males are indicated on the left and females on the right, like that pictured above.​

Concepts and Implications

Both age structure and age pyramids can take a variety of forms, depending on the birth and death trends within the population, as well as a host of other social factors. They can be stable, meaning that patterns of birth and death are unchanging over time; stationary, which signals both low birth and death rates (they slope gently inward and have a rounded top); expansive, which slope dramatically inward and upward from the base, indicate that a population has both high birth and death rates; or constrictive, which signal low birth and death rates, and expand outward from the base before sloping inward to achieve a rounded peak at the top.

The current U.S. age structure and pyramid, shown above, is a constrictive model, which is typical of developed countries where family planning practices are common and access to birth control is (ideally) easy, and where advanced medicine and treatments are commonly available through accessible and affordable healthcare (again, ideally). This pyramid shows us that the birth rate has slowed in recent years because we can see that there are more teens and young adults in the U.S. today than there are young children (the birth rate is lower today than it was in the past). That the pyramid moves stably upward through age 59, then only gradually shrinks inward through age 69, and only gets really narrow after age 79 shows us that people are living long lives, which means that the death rate is low. Advances in medicine and elder care over the years have produced this effect in developed countries.

The U.S. age pyramid also shows us how birth rates have shifted over the years. The millennial generation is now the largest in the U.S., but it is not so much larger than Generation X and the Baby Boomer generation, who are now in their 50s and 60s. This means that while birth rates have increased a bit over time, more recently they have declined. However, the death rate has declined considerably, which is why the pyramid looks the way it does.

Many social scientists and health care experts are concerned about current population trends in the U.S. because this large population of teens, adults, and older adults are likely to have long lives, which will put a strain on an already underfunded social security system.

It is implications like this that make the age structure an important tool for social scientists and policy-makers.